Longitudinal construct validity and responsiveness of measures of walking capacity in individuals with lumbar spinal stenosis
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BACKGROUND CONTEXT: Walking capacity is a primary outcome indicator for individuals with lumbar spinal stenosis (LSS). Therefore, there is a demand for psychometrically sound measures of walking that are responsive to change. PURPOSE: The primary objective of this study was to examine longitudinal construct validity of the Physical Function Scale of the Swiss Spinal Stenosis Questionnaire (PF Scale), the Oswestry Disability Index (ODI), and the walking capacity items from these scales specifically for the assessment of walking capacity in LSS using the objective Self-Paced Walking Test (SPWT) as the external standard. A secondary objective was to examine responsiveness of measures of walking using a self-reported walking capacity change scale as the external criterion standard. STUDY DESIGN: Patients were prospectively enrolled. PATIENT SAMPLE: Twenty-six patients were included in this study (17 women and 9 men), with an average age of 68.5 years (SD, 9.2). All participants had LSS diagnosed by a spine specialist surgeon based on both clinical examination and imaging, as well as self-reported walking limitations (neurogenic claudication). OUTCOME MEASURES: The self-reported outcome measures included in this study were PF Scale, ODI, and self-reported walking capacity change score. FUNCTIONAL MEASURES: The functional measure used in the study was SPWT. METHODS: Longitudinal construct validity was assessed using the correlational method. Internal responsiveness was examined using Guyatt responsiveness index and external responsiveness using receiver operating characteristic analysis. Change in the SPWT and the self-reported walking capacity change score were used as external criteria for the analysis. RESULTS: The highest correlations with change in the SPWT were 0.78 for the ODI walking item and 0.78 for the walking capacity change score. Changes in the PF Scale and ODI score were correlated with change in the criterion SPWT at r=0.56 and r=0.70, respectively. There were no differences observed between the PF Scale and ODI for any of the responsiveness indices. CONCLUSIONS: The PF Scale, ODI, and walking capacity change score are able to detect changes in walking capacity in people with LSS. The individual walking capacity item from the ODI appears to be the most valid and responsive to changes in measured walking and may be a reasonable alternative for measuring walking when an objective test such as the SPWT is not feasible.
